<template>
  <scroll
    @scroll="scroll"
    :listen-scroll="listenScroll"
    :probe-type="probeType"
    class="listview"
    ref="listview"
  >
  <ul>
    <li
      class="list-group"
      v-for="(group, index) in data"
      :key="index"
      ref="listGroup"
    >
      <h2 class="list-group-title">{{ group.title }}</h2>
      <ul>
      <li
        class="list-group-item"
        v-for="(item, index) in group.items"
        :key="index"
        @click="selectItem(item)"
      >
      <img class="avatar" v-lazy="item.avatar">
      <span class="name">{{ item.name }}</span>
      </li>
      </ul>
    </li>
  </ul>
  <div
    class="list-shortcut"
    @touchstart.stop.prevent="onTouchStart"
    @touchmove.stop.prevent="onTouchMove"
  >
    <ul>
      <li
        class="item"
        v-for="(item, index) in shortcutList"
        :key="index"
        :data-index="index"
        :class="{'current':currentIndex===index}"
      >
      {{ item }}
      </li>
    </ul>
  </div>
  <div class="list-fixed" ref="fixed" v-if="fixedTitle">
    <div class="fixed-title">{{ fixedTitle }}</div>
  </div>
  <div v-if="!data.length" class="loading-container">
    <loading></loading>
  </div>
  </scroll>
</template>
<script>
import Scroll from 'base/scroll/scroll'
import { getData } from 'common/js/dom'
import Loading from 'base/loading/loading'
const TITLE_HEIGHT = 30
const ANCHOR_HEIGHT = 18
export default {
  name: 'listview',
  props: {
    data: {
      type: Array,
      default () {
        return []
      }
    }
  },
  data () {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    }
  },
  computed: {
    shortcutList () {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle () {
      if (this.scrollY > 0) {
        return ''
      }
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    refresh () {
      this.$refs.listview.refresh()
    },
    selectItem (item) {
      this.$emit('select', item)
      // this.$router.push(`/singer/${item.id}`)
    },
    _calculateHeight () {
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
    },
    scroll (pos) {
      this.scrollY = pos.y
    },
    _scrollTo (index) {
      if (!index && index !== 0) {
        return false
      }
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    },
    onTouchMove (e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    onTouchStart (e) {
      let anchorIndex = getData(e.target, 'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    }
  },
  components: {
    Scroll,
    Loading
  },
  created () {
    this.probeType = 3
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
  },
  watch: {
    diff (newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
    },
    data () {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY (newY) {
      const listHeight = this.listHeight
      // 当滚动到顶部，newY>0
      if (newY > 0) {
        this.currentIndex = 0
        return false
      }
      // 在中间部分滚动
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          this.diff = height2 + newY
          return
        }
      }
      // 当滚动到底部，且-newY大于最后一个元素的上限
      this.currentIndex = listHeight.length - 2
    }
  }
}
</script>
<style lang="stylus" scoped>
@import "~common/stylus/variable"
.listview
  position: relative
  width: 100%
  height: 100%
  overflow: hidden
  background: $color-background
  .list-group
    padding-bottom: 30px;
    .list-group-title
      height: 30px
      line-height: 30px
      padding-left: 20px
      font-size: $font-size-small
      color: $color-text-l
      background: $color-highlight-background
    .list-group-item
      display: flex
      align-items: center
      padding: 20px 0 0 30px
      .avatar
        width: 50px
        height: 50px
        border-radius: 50%
      .name
        margin-left: 20px
        color: $color-text-l
        font-size: $font-size-medium
  .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: -1px
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
